The causes of musculoskeletal pain include injury, degenerative joint disease and overuse injuries. Such pain affects the vast majority of the population at some time and in some form and may impact significantly on a sufferers quality of life and personal productivity. The generalised incidence and variable severity of such pain results in a significant cost for society.
Persistent musculoskeletal pain is increasingly identified as originating from joints as a result of poor muscle control of relevant muscles with associated poor joint stability. There is clear evidence linking restoration of stability of the joints with resulting pain control. Various muscles are used to protect and control any particular joint. Some are deep and close to the joint ("deep muscles") while others are often larger and further away from the joint but still exert an influence on the joint ("superficial muscles"). The joint stabilising function of these muscles can be divided into two basic components being the timing of muscle contraction and the manner of muscle contraction, particularly in relation to other muscles. As a result of the increasing awareness of causation of joint pain, its management has been directed towards improving the stabilising function of the muscle system and its ability to protect and support the joints. Various assessment, prevention and rehabilitation programmes have been implemented at considerable cost but with little systematic or objective appraisal of the results on joint stabilisation and efficacy in relieving pain. The main limiting problem in objective assessment of joint function and assessment of response to treatment is the absence of practical methods of in vivo assessment to enable evaluation of the stabilising capacity of the most relevant muscles. Some attempts have been made to address this deficiency.
Australian Patent AU 657277 describes a pressure biofeedback apparatus which permits monitoring of performance of physiotherapy exercises and enables the checking of compliance with prescribed instructions. The purpose is to ensure correct muscle action during exercise and also to ensure safety and precision of stretching techniques. While important in the described function, the device does not give a reliable indication of specific deep muscle function or the activity of such a deep muscle or muscles in relation to other muscles.
Use of pressure biofeedback monitoring with abdominal drawing in exercises is known. Similarly, pressure biofeedback has been used during abdominal drawing in exercises in lower back pain in combination with electromyographic ("EMG") biofeedback monitoring of the rectus abdominis and obliquus abdominis externus to confirm that the drawing in action is being produced by the deep abdominals with minimal activation of the large superficial muscles. (Richardson C A, Jull G A: An historical perspective on the development of clinical techniques to evaluate and treat the active stabilizing system of the lumbar spine. Australian Journal of Physiotherapy Monograph No 1 at 8, 1995) Use of this technique however requires a level of specialist training above that of an average practicing physiotherapist as the technique is prone to inaccuracies which can only be detected by subtle clinical signs. Clinical proficiency in assessing deep muscle function requires skills based on a knowledge of the principles of motor learning as well as skills to detect when substitution strategies are being used for an action.
U.S. Pat. No. 4,592,371 describes a simple pressure recording device to allow a gross measurement of pressure and duration created by the recruitment of large muscle masses such as an entire limb and is a basic indicator of large muscle group performance. It is of little use in deep muscle assessment.
WO 96/29929 discloses a diagnostic apparatus for the diagnosis of lower back pain which relies on comparison of the timing of contraction initiation in an anticipatory muscle and in a prime mover muscle. Use of the disclosed apparatus, however, relies principally on insertion of fine wire electrodes in the deep muscles of interest and comparison of muscle function is restricted to relative times. The clinician obtains an indication of muscle function and the technique is of great use in lower back pain but suffers from the disadvantage of its invasiveness.
Use of real-time ultrasound to view muscle contraction is known and has been used to provide biofeedback to both clinicians and patients. (Hides J A, Richardson C A, Jull G A, Davies S: Ultrasound imaging in rehabilitation, Australian Physiotherapy 41:187, 1995). This technique has the benefit of visualization of specific muscle contraction coupled with the ability to determine the duration of contraction. However, it does not provide an indication of the extent of utilization of other superficial muscles to the activity nor does it give a quantification of the contraction of the deep muscle.
Clearly there is a need for an apparatus or method of assessment which gives an objective measurement of the function of the muscular support of a joint or joints and which preferably is non-invasive. Such an apparatus or method could be used as an aid in diagnosing lack of stability, assessing the specificity of a remedial exercise programme and monitoring improvement subsequent to therapeutic invention. There is also a need for a non-invasive technique to assess the function of deep muscles without the requirement of specialized training of the operator.